1. Field of Invention
The present invention relates to the field of an electro-optical device, such as a liquid crystal device or the like, and an electronic apparatus. The present invention also relates to the field of electrophoresis devices, such as electronic paper or the like or EL (electro-luminescence) devices or devices using electron emission devices (Field Emission Displays and Surface Conduction Electron-Emitter Displays) and the like.
2. Description of Related Art
In the related art, there have been known electro-optical devices, such as liquid crystal devices including an electro-optical substance, such as liquid crystal or the like held between a pair of substrates, whereby display of images is enabled by transmitting light so as to pass therethrough. Now, “display of images” is, for example, realized by changing the transmissivity of light by changing the state of the electro-optical substance for each pixel, thereby visualizing light with a different gradient for each pixel.
Such electro-optical devices being provided include active-matrix drivable arrangements including, on one of the pair of substrate, pixel electrodes arrayed in matrix fashion, scanning lines and data lines provided weaving between the pixel electrodes, and further, TFTs (Thin Film Transistor) and the like, serving as pixel switching devices. With the active-matrix drivable electro-optical devices, the TFTs are provided between the pixel electrodes and data lines, and control conduction therebetween. Also, the TFTs are also electrically connected to the scanning lines and data lines. Thus, it is possible to control turning the TFT on and off through the scanning lines, and also in the event that the TFT is on, an image signal supplied through the data line can be applied to the pixel electrode, i.e., the light transmissivity can be changed for each pixel.
With such electro-optical devices, the above-described configuration is fabricated on one of the substrates, but this requires a great area if laid out two-dimensionally, which could reduce the pixel opening ratio, i.e., the ratio of the area which light is to be transmitted through as to the area of the entire substrate. Accordingly, techniques for configuring the above-described components three-dimensionally, i.e., techniques for layering the components by introducing an inter-layer insulating film therebetween have been used with related art arrangements as well. More specifically, first, the TFTs and scanning lines functioning as gate electrode film for the TFTs are formed on the substrate, upon which are formed the data lines, and further thereupon the pixel electrodes and so forth. This way, in addition to reduction in the size of the device, enhanced pixel opening ratio and so forth can be achieved by suitably setting the array of the components.
Now, with such electro-optical devices, there is a basic demand for displaying high-quality images, and with regard to achieving this, higher opening ratio and higher contrast of images and the like are demanded in particular of the electro-optical devices. Here, “opening ratio” can be expressed by the ratio or the like of the ratio of light transmitting areas as to the entire area of the substrate making up the electro-optical device or the entire area of the image display region on the substrate, and the higher this value is, the brighter the image is. Also, increasing the contrast of the image is achieved by electrically connecting capacitors to the TFTs and pixel electrodes for example, thereby increasing the potential holding properties of the pixel electrodes.
On the other hand, further reduction in size and increased precision, and driving at higher frequency are being demanded of the electro-optical devices. However, attempting to achieve the above-described increase in opening ratio and reduction in size is met with difficulties. The reason is that an opening ratio of a certain level or more is necessary to display images with a certain level of brightness or more, so the area of the light transmission region needs to be kept around the same, which contradicts the reduction in the substrate area which occurs if the size is reduced. That is to say, in this case, an essential increase in the area of the light transmission region is being demanded.
Also, simply essentially increasing the area of the light transmission region is not sufficient to achieve a high opening ratio. This is because that would affect the surrounding configuration. For example, as described above, capacitor is provided in some cases with electro-optical devices to increase the contrast, but in order to achieve a high opening ratio based upon the assumption that such capacitor exists, the capacitor needs to be narrowed down. However, simply narrowing down the capacitor leads to high resistance at the pair of electrodes configuring it at a proportionate amount, which leads to new problems such as cross-talking and burn-in caused thereby. Now, there have been related art examples wherein the pair of electrodes were formed of polysilicon or WSi (tungsten silicide) or the like, but the resistance of these materials is by no means low, making the above problem even more serious.
Moreover, in addition to the above-described capacitors, TFTs serving as pixel switching devices are provided on the substrate, there is the need to arrange such that there is no light cast into the TFTs or the semiconductor layer thereof when achieving a high opening ratio. This is because such light cast therein can cause flickering or the like on the image due to a photo-leak current occurring at the semiconductor layer. In realizing a high opening ratio, the area of the light shielded regions is generally expected to be reduced relative to the area of the light transmitting region, so the above-described problem has even more serious aspects. That is to say, the danger of light being cast into the semiconductor layer is even greater.
As described above, measures for simply increasing the area of the light transmitting region cannot achieve higher opening ratio, and total measures for all aspects need to be taken to achieve this object.